Seriously, this is getting out of control. Every day random people (or bots) sign up on the forum just to post crap in the job boards. I wouldn’t mind if it would be serious request or offers, but 99% of them are just plain bullcrap.
A while ago somebody (I believe Derek) said that captcha’s were added, and while they did lower the amount of spam, they did not prevent these bots/people/idiots (or whatever they are) from posting in the job boards.
While it is really difficult, if not impossible to block these posts, it is possible to prevent people from signing up and spamming the job board forum straight away. Simply restrict access to the job boards to those who have less than X posts.
To cut a long story short, get rid of these people and prevent them from coming back.